The invention generally pertains to the field of water treatments, e.g. waste water treatments. The water treatable by the present invention includes, for instance, sewage, breeding waste water, hog breeding waste water, human waste water, household waste water, agriculture waste water, starch industry waste water, food processing waste water and forestry waste water. The invention concerns a method for treating such water by activated sludge. The method according to the invention comprises environmentally adapting (or acclimatizing) micro-organisms, and nitrifying and de-nitrifying the waste water by these acclimatised micro-organisms. The particularities of the present method consist, inter alia, of causing a series of reactions in the same reactor, preferably under strong aeration at the acclimatization stage of the treatment.
In the past, many scientists have researched into nitrification and de-nitrification reactions taking place in micro-organisms, in order to elucidate the nitrogen cycle. A large part of the results obtained were reviewed by A. J. Kluyver and C. B. von Niel in a book entitled “The Microbe's Contribution to Biology” published in 1956 by Harvard University Press, Cambridge Mass. USA. This review gives experimental details on the environmental conditions for growing micro-organisms and on their capacity to adapt to the environments.
The methods for analysing the sludge piled up in polluted closed water systems were developed by The Environment Agency of Japan and published in 1985 by The Japanese Society for Environmental Analysis in a report entitled “Ways of Evaluating Underwater Sediments and Commentary on the Results”.
Further, microbial de-nitrification reactions were applied to waste water treatments by H. Kishi, and the results were published in 1985 in a document entitled “Hybrid Lagoon System” edited by Rural Environment Research Association, Tokyo, Japan. This document discloses a newly modeled water-utilisation system, in which specific measuring and aeration apparatuses are applied for controlling the waste water treatment. Those apparatuses are required for implementing microbial de-nitrification technologies and establishing efficient waste-water treatment technologies.
Further yet, a new waste-water treatment process was conceived and applied to microbial de-nitrification reactions, and the results obtained were published by H. Kishi in 1991 in a report entitled “Experimental Report on Water-Bottom Sediment Purification in Marsh Furukawa”, edited by Ministry of Transport. 15th US-JAPAN Expert Meeting. According to this report, noxious underwater sediments could be recovered as biologically activated sludge containing abundant oxygen, and returned to a closed water system. Accordingly, the problem of sludge devoid of oxygen was solved and a new bionomical system was created.
In the above prior arts, the de-nitrification installations are conceived on the basis of a continuous activated sludge method. Such methods generally involve a series of installations, i.e. a BOD-removing installation, a nitrification installation and a de-nitrification installation. In other words, three reactions are carried out in separate reactors.
However, the above-mentioned continuous de-nitrification installations require a complicated construction and many types of reagents and, as a result, consume a considerable amount of energy.
For instance, there exists a three-step de-nitrification system, in which a BOD removal reactor, a nitrification reactor and a de-nitrification reactor are arranged in series. This system, tried in the USA, requires complicated devices, and methanol has to be added. Moreover, it consumes a lot of energy and increases social burdens.
Recently, there have also been conceived waste-water treatment sites based on the principle of half-feed-back-type activated sludge method. The reactor used in this method is called “Semi-Batch Reactor” and referred to as “SBR”. According to this principle, the nature of waste water is analysed beforehand, and optimization conditions for waste water treatments are simulated using a model. The model is then used as know how.
The system “SBR” is controlled by introducing a factor of time and carrying out intermittent aerations. Such a controlling method, though automatically operated, requires the de-nitrification reaction to be caused under predetermined conditions. Accordingly, this method is not based on an automatic control system, in which parameters under running conditions are fed-back in real time. As a result, the system cannot maintain the optimum conditions when confronted with external or internal turbulences or variations.
There thus exists no technology according to which data on microbial reactions are fed back without using mathematical or logical analysis and further, microbial de-nitrification reactions are completely self-controlled.
By contrast, according to the invention, activated sludge is adapted so as to acquire both nitrification and de-nitrification functions that co-exist in a single reactor or lagoon. The activated sludge also becomes self-responsive to variations of the external parameters such as quantities, substrates and temperatures of the activated sludge. Further, the technology of the invention enables microbial de-nitrification activities to be maintained at high level.